Arthropods

Digestive system-
Paired appendages around the mouth are used for collecting and handling food and are usually specialized in accordance with the particular diet of the animal.
Nervous system-
Their nervous system is "ladder like," with two ventral nerve crods running through all segments and forming two ganglia in each segment.
Body plan-
  • exoskeleton (a skeleton on the outside of the body)
  • body divided into distinct parts
  • jointed legs and appendages
  • bilateral symmetry (both sides of the body are the same)

Picture-

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http://www.biologycorner.com/bio1/notes-arthropods.html

Positive impact on humans
-link in food chain
-pollination, most seed plants would not exist, ~65% insect pol.
-human food, specifically crustaceans, several million pounds annually
from Gulf of Mexico alone (primarily shrimp)
-silk
-spider silk can be stronger than steel of the same gauge.
-insectivorous arthropods help control insect pests Ex. lady bug
-soil dwelling arthropods scavengers and decomposers
-Esthetic and psychological
Negative impact on humans
-Ticks
-Mites
-Mosquitoes
-Fleas
-Lice; look upon people, their pets and livestock as just another meal (parasitic larva can also be involved)
-Painful bites of stings in self-defense, more people die of bee and scorpion stings than by snakebite (or shark attacks!)
1 interesting fact
They first evolved about 445 million years ago during the Late Ordovician Period.